The motor driven vehicle, as is well known, has achieved substantial success as a means for transporting cargo. In many phases of industry it is imperative that the vehicle carry larger loads than heretofore deemed necessary or capable of economical handling. In general, larger loads require larger trucks and more load supporting axles. In addition to the requirement that the vehicle carry larger loads there are many portions of the industry where the vehicle must retain its maneuverability, a requirement in direct conflict with the greater size required.
A prime example of a particular industry wherein the vehicle is required to carry maximum loads and yet maintain maximum versatility in terms of positioning is the mining industry. An ore loader or the like must be able to maneuver sharp corners with minimal clearance within mining tunnels. Yet another industry which has similar requirements is the logging industry wherein the roads serpentine between trees and rock outcroppings. Still a further example of an industry requiring maximum loads and maximum versatility is the construction related industries requiring vehicles such as cement trucks to be able to deliver their loads to sites having very difficult access.
Particularly directing our comments to mining many vehicles have gone to both articulated frames and individually driven wheels in an attempt to satisfy the requirements. Another attempt to satisfy industry requirements is seen in tractor driven trailers wherein the wheels of a trailer are mounted upon a boggie which may be remotely steered from the vehicle thereby permitting the operator to have far greater maneuverability of his vehicle.
Still other vehicles have been designed wherein more than one set of wheels is capable of being steered and under the control of the operator.
Prior art references known to the inventor which deal with either modified suspension or multiple steerable wheels include U.S. Pat. No. 2,532,151 granted to Dibert et al Nov. 28, 1950 which teaches the concept of a steerable rear boggie for use with a trailer wherein the operator can direct fluid under pressure to pivot the boggie mounted upon a turntable beneath the frame of the trailer.
U.S. Pat. No. 2,648,392 granted to Brown Aug. 11, 1953 teaches the concept of mounting a truck cab and engine upon a trailer frame and having front wheels mounted on a turntable beneath the cab and thus pivotally rotatable with respect thereto.
U.S. Pat. No. 2,906,358 granted to Tucker Sr. Sept. 29, 1959 discloses a multiple rear wheel vehicle wherein two sets of boggies are mounted beneath the frame and each are rotatable with respect to the frame and driven by means of an interconnecting chain drive.
U.S. Pat. No. 3,048,422 granted to Payne et al Aug. 7, 1962 disclosing a steerable trailer having the rear wheels mounted upon a boggie which is pivotable relative to the trailer frame by means of forwardly extending arm and a fluid powered ram.
U.S. Pat. No. 3,591,203 granted to Steiner July 6, 1971 teaches a steering system for steerable rear wheels of a trailer vehicle. A sending piston cylinder arrangement is connected to the front wheels of the trailer and the output therefrom is connected to the rear wheels assuring that as the towing vehicle turns the towed vehicle assumes a tracking orientation.
U.S. Pat. No. 3,873,129 granted to Schmidt Mar. 25, 1975 discloses a steerable log trailer having a pivotal rear boggie movable relative to the reach guide and controlled by a pair of opposing fluid cylinders mounted to the reach guide.
U.S. Pat. No. 3,981,512 granted to Westover on Sept. 21, 1976 discloses a rear wheel steering system for trailers wherein the rear wheels are supported upon a boggie which is movable relative to the frame and kept in position by guide pins serving as followers within a groove in an overlying plate.
U.S. Pat. No. 4,010,816 granted Mar. 8, 1977 to Powell discloses the utilization of two fluid operating cylinder assemblies secured between the bunk of a trailer and the rear frame position enabling controlled relative movement between the frame portion and the load. The cylinder assemblies are actuated independently of the engine and the steering mechanism and fluid under pressure is applied by a pump driven by electric motor mounted to the trailer itself.